Casings or cases such as those for rocket motor combustion chambers or war heads which contain heat sensitive energetic materials such as propellant grains or explosive material present a serious safety hazard. If the casing should be exposed to fire or other high temperature environments when not in use, an explosion may result. Under these conditions, the heat sensitive energetic material within the casing can ignite and cause catastrophic thermal stress and pressure buildup within the case with subsequent explosion. Responsive to this hazard, military tests and specifications have been developed to assure that these types of rocket motor combustion chambers or warheads are designed so that these types of hazards do not occur as a result of fires, other high temperature environments or penetration of the casing by a bullet or other high speed fragment.
The prior art has proposed various solutions to avoid case explosions when subjected to such things as fuel fire, cook-off conditions or projectile and/or shock scenarios. For example, U.S. Pat. No. 4,458,482 to Vetter et al. discloses a rocket motor which will undergo a small local case rupture and produce a mild burning reaction to prevent a dangerous build-up of interior pressure.
U.S. Pat. No. 4,041,869 to San Miguel discloses a rocket motor casing using a “cook-off liners” with discontinuities therein to allow room for a thermal expansion of propellant grain or the cook-off liner without significantly reducing the protection of the rocket motor.
U.S. Pat. No. 5,170,007 to Figge discloses a tailorable, roll-bonded, insensitive munitions case which loses its structural integrity upon reaching a predetermined temperature which is below the auto ignition temperature of the housed heat-sensitive energetic material. This patent is incorporated by reference in its entirety herein.
Although various solutions have been proposed to overcome the problems discussed above with these types of cases, the prior art still includes numerous disadvantages. Many of the prior art designs are costly to manufacture in that detailed and complicated machining is required to meet the insensitive munition guidelines. Moreover, the prior art designs are typically rigid in nature and do not offer a wide flexibility in accommodating different size cases and/or different types of heat sensitive energetic materials.
In view of these disadvantages, a need has developed to provide an improved rocket motor case which meets the insensitive munition guidelines but is lower in cost to manufacture and more flexible in meeting various design specifications. Responsive to this need, the present invention provides an improved rocket motor case which utilizes plank sections which are easily configured to a given motor case design. The plank sections, in combination with roll bonded sheets, offer both passive and active case venting prior to propellant cook-off.